1. Field of the Invention
The invention relates to a motor control device.
2. Description of the Related Art
As an example of a motor control device, an electric power steering system (EPS) for a vehicle is known. The electric power steering system is configured such that a torque sensor detects a steering torque applied to a steering shaft at the time of steering, and an assist control circuit calculates an assist command value, which is a control desired value for an electric motor (hereinafter, referred to as “motor”), based on the steering torque or based on the steering torque and a vehicle speed from a vehicle speed sensor.
Further, the electric power steering system is configured such that a motor control circuit calculates a motor current command value on the basis of the assist command value, and a motor driver outputs a motor current based on the motor current command value to the motor, thereby driving the motor. In recent years, some vehicles are provided with an automatic steering system that assists a driver's operation, such as an advanced driver assistance system (ADAS). In this automatic steering system, in order to improve a driver's steering feel and to perform automatic steering, a motor of an EPS is controlled on the basis of, for example, a command value based on steering performed by the driver, a command value based on an environment surrounding a host vehicle, which is measured by a measurement device, such as a camera or a radar.
In order to cope with, for example, automatic driving as described above, an electric power steering system having a redundant system configuration is proposed (see Japanese Patent Application Publication No. 2004-10024). This electric power steering system includes two systems each including sensors, an assist control circuit, a motor control circuit, a motor driver, and a motor, which are configured as described above. This redundant system configuration enables more stable motor control.
However, even when the redundant system configuration is employed, the following unfavorable situation may occur. That is, if the steering torques, or the vehicle speeds detected by the sensors for the respective systems are different from each other, different motor current command values are output to the motors of the respective systems based on command values, such as assist current command values, which are calculated in the respective systems. It is not preferable that there is a difference in command value between the two systems.